M4300 Stack (GSM4253PB) - Firmware upgrade causing PABX failure ?

Hi. 

We have a stack of 4 GSM4253PB switches with firmware version 12.0.11.15 and yesterday we planned an upgrade to version 12.0.19.4, going through the versions :
12.0.11.15 -> 12.0.13.8
12.0.13.8 -> 12.0.15.7
12.0.15.7 -> 12.0.17.6
12.0.17.6 -> 12.0.19.4
At each version upgrade, we carried out a complete stack update (simultaneous restart of the stack).

The firmware was copied to the stack via the web console (http upgrade) on the inactive image with Stack Firmware Auto Upgrade enabled.
On two occasions, the firmware copy had to be restarted because it was frozen.
After the last reboot of the stack, the master changed and the LAG of 2 cables uplinking toward the core stack was unstable (one member had been changed from 1/0/51 to 3/0/51, a port on which there was no cable...).

After correcting these two incidents, I realised that the VLAN configurations of switches 1 (master) and 4 (member) had been lost, causing a network loop. This was quickly corrected.

Subsequently, the OmniPCX PBX connected directly to this stack failed: the CPU card was blinking orange and the LAN ports were unreachable. According to Alcatel-Lucent technical support, a ‘network anomaly’ caused the CPU card to flash its firmware (!!!) and rendered the PBX inoperable. This card controls power-up and the other ports are no longer powered => no diag possible.

Do you think this can really happen ? Is this a plausible cause of the failure ? Can you imagine what had possibily went so wrong that this PABX stopped functionning because of a switching stack firmware upgrade ?

Any help or insight would be appreciated. I hope this case is clear enough.

Regards.